Exchanges with the Environment (UNIT 2 RECAP)• - Understand what materials need to be

exchanged: respiratory gases, nutrients and excretory products

• Understand the relationship of size and surface area to volume ratio

• Understand the features of exchange surfaces which aid passive and active transport

• Understand the special features of gas exchange surfaces

• Understand the need for ventilation mechanisms

• Gas exchange in protozoa, humans, and plants

Gas exchange in Humans

• Recall the structure of the thorax: understand the mechanism of ventilation, including the role of the pleural membranes

• Understand how breathing is controlled:understand vital capacity and tidal volume

• Recall the structure of an alveoli and understand their role in gas exchange, explain the function of surfactants:know that breathing is controlled but the respiratory centre in the brain.

Exchanges with the environment:

• Relationship between surface area/volume (size of cells)

• Need for ventilation mechanisms

• Features of gas exchange surfaces

• Gas exchange in protozoa

• Gas exchange in humans

• Mechanism of ventilation

• Control of breathing

• Vital capacity and tidal volume

• Role of alveoli in gas exchange

Imagine if these were unicellular organisms . . Problems?/solutions

Other examples of cells/organisms which are adapted with a larger surface area?

Protozoa

What materials do they need to exchange?

How is this achieved?

Why are there not large unicelluar organisms?

Mammalian Gas Exchange surface – the lungs

Features of gas Exchange surfaces

• Large surface area to volume ratio

• Partially Permeable

• Thin (short distance for diffusion 0r active transport)

• May be covered with a film of moisture (although this makes diffusion slower, but easier)

• Diffusion gradients

Pulmonary System(unit 4)-Recall the structure of the structure of the breathing system and the mechanism of ventilation-Understand the histology of lung tissue-Understand how the ventilation mechanism is controlled: -the roles of respiratory gases: the control centres in the medulla, stretch receptors and cranial nerves

Structure of the Lungs

Mammalian Gas Exchange surface – the lungs

Mammalian Gas Exchange surface – the lungs

Epithelial Cells – their adaptations

These 2 types of specialised epithelial cells are found in the respiratory tract until the bronchioles and alveoli duct. Can you think why you wouldn’t find them further?

Histology of the Lungs – detail alveoli and capillaries

Squamous Epithelium

The table below refers to three differences of epithelia. Complete the table by writing the name of each type of epithelium and giving one location of each.

Epithelium Name One location

   

   

   

• Describe two ways in which alveoli are adapted to their function

1. The diagram below shows a section through lung tissue, as seen using a microscope.(a) Explain how the cells labelled A are adapted to their function.

  

• large surface area ; increases diffusion ;

• thin (wall) / single cell ;reduces diffusion distance ;

• reference to surfactant ; stops adhesion ;

• reference to capillaries ; maintains, diffusion /concentration gradient

An Overview of Respiratory Processes and Partial Pressures in Respiration

PO2 and PCO2 are arbitrary units and for comparison of concentration

Gas exchange across respiratory membrane is efficient due to:• Differences in partial pressure (concentration

gradients)• Small diffusion distance 6μm• Squamous epithelium• Lipid-soluble gases• Large surface area of all alveoli• ( be careful - Moist membrane – although this

actually slows down gas diffusion)• Coordination between blood flow and airflow

Diffusion and respiratory function

Figure 23.17a-d

The Respiratory Muscles

• Movement of air depends upon

• Pressure and volume - inverse relationship

• Volume depends on movement of diaphragm and ribs to create changes in volume and so pressure

Changes in pressure cause movement of air in/out

Ventilation of the lungs

Respiratory Pressure and Volume Relationships

Mechanisms of Pulmonary Ventilation

• Normal breathing involves the diaphragm muscle, the external and internal intercostal muscles

• Forced breathing involves additional contractions of the Abdominal muscles

• Inhalation • Diaphragm and External

intercostal muscles contract• Volume in thorax increases• Pressure lowers• Air is drawn into lungs

Mechanisms of breathing

Exam Question

• 1. (a) State three characteristic features of gas exchange surfaces.

• 1 …………………………………………………………………………………….

• 2 …………………………………………………………………………………….

• 3 …………………………………………………………………………………….

• (3)

• (b) Describe how the process of inspiration (breathing in) takes place in mammals.

• (3)

(Total 6 marks)

Answers!• 1. (a) State three characteristic features of gas

exchange surfaces.

• large surface area;

• thin lining;

• (partially) permeable (lining);

• covered by film of moisture.

• (3 marks)

• 3 Describe how the process of inspiration (breathing in) takes place

in mammals.

• contraction of diaphragm muscles lowers / flattens diaphragm;

contraction of external intercostal muscles raises ribcage;

volume of thorax / lungs increases thus intrapulmonic pressure

falls / eq.reference to control by medulla / eq.

• (3 marks)

• [Total 6 marks]

•  

•  

Soda lime removes CO2 which may be harmful if repeatedly breathed in and allows volume of oxygen used to be established With nose

clip!

Chamber filled with oxygen

Needs calibration first with know volumes of oxygen

Spirometer – calculations of ventilation volume and rate

• Alveolar volume-Amount of air reaching the alveoli each minute

• Tidal Volume (VT)

-Amount of air inhaled or exhaled with each breath• Vital capacity

-Tidal volume plus expiratory and inspiratory reserve volumes

• Residual volume-Air left in lungs after maximum exhalation

Respiratory volumes

Respiratory Volumes and Capacities

• Tidal Volume (VT)

-Amount of air inhaled or exhaled with each breath. In normal Quiet breathing (male) 500cm3.

• Alveolar volume

-Amount of air reaching the alveoli each minute – 350cm3. (remaining is in trachea, bronchi etc and is called the dead air volume). Mixes with the air from previous inspiration and air undergone gaseous exchange – this keeps the oxygen level constant throughout the breathing cycle

• Inspiratory/Expiratory Reserve volume

When maximum breathing in (up to 2000cm3)

Maximum breathing out (up to 1500cm3)

Residue air (prevention of lung collapse 500cm3)

• Vital capacity

-Tidal volume plus expiratory and inspiratory reserve volumes (up to 400cm3)

• Residual volume

-Air left in lungs after maximum exhalation

Respiratory volumes

Control of Ventilation Rates

External Intercostal muscles and diaphragmDown Phrenic nerve

Respiratory centers – which control breathing rates- are modified by sensory information including:

1. Chemoreceptors from carotid arteries(from heart)

-Level of carbon dioxide (partial pressures of CO2) cause increase of respiration rates. pH changes

2. Baroreceptors (blood pressure)in carotid arteries

3. Stretch receptors in Lungs which controls the Hering-Breuer reflexes

-Prevents over-inflation and potential damage

Respiratory control and reflexes

Exercise Causes:

Increased adrenalin

Increase in CO2 in blood

Lowering of pH

Detection by chemoreceptors in Carotid artery

Stimulates breathing centres in Medulla

Medulla Responses:

Increase the frequency of impulses to diaphragm and intercostal muscles for increased contraction/relaxation

Effect of Exercise on ventilation rate

• Breaths per min increases

• Ventilation rate increases

• Tidal volume increases

• Greater variation in volumes between inspiration and expiration

• Decreases the inspiratory reserve volume as tidal volume increases

Adrenaline released

Glycogen Glucose gluconeogen-esis

Constriction of skin and gut

arterioles

Fatty acids mobilised from

fat stores

Dilation of muscle

arterioles

Before the race…

…your system starts to prepare.

Several minutes later… Anaerobic respiration

produces Lactate – this stimulates

further dilation of arterioles

Increased CO2 raises

breathing and pulse rates

Adrenaline dilates

bronchioles

…you return to aerobic respiration and “get your second wind”.

Vo2 reaches Vo2max

Effects of training on ventilation rate

• Increase in tidal volume after exercise not as great

• Increase in ventilation after exercise not as great

• Faster return to normal breathing patterns

• Respiratory muscles stronger (intercostal, diaphragm, abdominal muscles)

• Alveolar capillary network increased

The Chemoreceptor Response to Changes in PCO2

Autonomic Nervous System

Figure 23.24

Figure 23.24 Carbon Dioxide Transport in Blood

• Homeostatic mechanisms maintain balance

• Local regulation of gas transport and alveolar function include

• Lung perfusion

• Alveolar capillaries constrict in low oxygen

• Alveolar ventilation

• Bronchioles dilate in high carbon dioxiRespiratory Centers and Reflex Controls

Gas absorption/generation balanced by capillary rates of delivery/removal